Fluke P3100 Series User Manual page 29

The design of a Piston/Cylinder Unit (PCU) fitted to a deadweight tester
allows for a very small clearance gap between the piston and cylinder.
This is required to allow the working fluid to pass between the components,
providing a lubricating film, and preventing metal-to-metal contact.
Therefore, during the normal operation of a deadweight tester, the working
fluid in the system will be slowly passed through this clearance gap. This is
perfectly normal, and does not mean that the system is leaking. However,
over time, it will collect and run down the side of the PCU mounting bodies.
The design of this instrument includes Sump Rings around the base of the
PCU mounting bodies to collect the excess fluid—these should be wiped
clean periodically to avoid overflowing on to the instrument top plate.
The sump ring is also fitted at the base of the test station, as it is common
for fluid to fall from the DUT when it is disconnected from the instrument
after calibration. This should also be kept clean to prevent spills on the top
plate.
Correct Operation of Water-Operated Instruments (3200 Series):
To avoid damage to the sensitive PCUs, it is vital to ensure that
there is a continuous film of water between piston and cylinder.
Due to the very close fit of these components, the water film
can break down very quickly after use, due to evaporation,
surface tension and capillary action effects.
Before using the instrument after a period of inactivity:
•
Low Pressure: Hold the weight carrier table and gently lift the piston assembly
vertically, slowly turning to check for freedom of movement.
•
High Pressure: Lift off the weight carrier tube assembly. Hold the piston cap and
gently lift the piston assembly vertically, slowly turning to check for freedom of
movement.
UNDER NO CIRCUMSTANCES should excessive force be used
on the piston assembly as this may lead to permanent damage.
IT SHOULD NEVER be forced, or pulled, in such a way that a
bending movement is applied to it.
•
To aid in piston lubrication and movement, it is sometimes helpful to gently
pressurize the system to a maximum of 15 psi/1 bar.
•
If any resistance or "grittiness" is felt, the PCU has either dried out too much to use
in its current condition or the system has been contaminated. In either case, the PCU
must be removed and dismantled for cleaning, see Chapter 6.
If, after cleaning, the PCU's performance deteriorates quickly, it confirms that the system
is contaminated. If this is the case, the instrument must be completely dismantled and
cleaned before further operation of the PCU assembly.
Note
W Caution
W Caution
Operation
4
Operation
4-3